67 kDa laminin receptor (hereinafter it may be referred to as “67LR”) is a protein of 67 kDa, which is derived from a 37 kDa precursor protein translated from mRNA that codes for 295 amino acids, through intracellular acylation polymerization of the precursor protein by a fatty acid for homo-dimerization or hetero-dimerization thereof; and only when it moves onto the surface of a cell membrane together with integlins, it functions as a laminin receptor (Biochemistry, 1995, 34: 11276-11287, T. H. Landowski et al.; J. Cell. Biochem., 1998, 69: 244-251, S. Buto et al.). It has been clarified that the 37 kDa precursor protein participates in protein synthesis as a ribosome-related protein p40 and it is the same as that reported as a multidrug resistance-related protein (MGr1-Ag) (Cell. Mol. Life Sci., 2002, 59: 1577-1583, Y. Shi et al.). From the data of its high expression in many types of cancer cells, the laminin receptor is considered to be an oncofetal antigen as an immunogen for T cells, or that is, as a general tumor-specific transplantation antigen (Anticancer Research, 1999, 19: 5535-5542, J. H. Coggin, Jr., et al.). In addition to 67LR, a dozen or so types of laminin receptors have been already reported, and of those, the relationship between 67LR and cancer is strongly suggested.
Based on detection or non-detection thereof in cancer cells, 67LR is known as an important prognostic factor in many types of cancers that indicates the degree of malignancy of human cancer patients (Breast Cancer Research and Treatment, 1998, 52: 137-145, S. Menard, et al.; Clinical Cancer Research, 1997, 3: 227-231, G. Fontanini, et al.; Clinical Cancer Research, 1996, 2: 1777-1780, F. Basolo, et al.; J. Natl. Cancer Inst., 1991, 83: 29-36, V. Coice, et al.). In animal models, it is suggested that 67LR participates in proliferation, movement, invasion and metastasis of cancer cells. For example, it is reported that the survival rate of 67LR-positive breast cancer patients is significantly lower than that of 67LR-negative ones. It is shown that the expression of laminin, the ligand of 67LR, has no influence on prognosis but the expression of the receptor 67LR brings about a negative result in prognosis (Breast Cancer Research and Treatment, 1998, 52: 137-145, S. Menard, et al.).
Some experiments have been reported, on the basis of this information and with expectation of an antitumor effect by inhibiting 67LR expression. It is reported that a 67LR low-expression cell line constructed by introduction of an antisense RNA of 67LR into a cancer cell line shows in-vivo significant depression of tumor proliferation capability and depression of metastasis capability in mice, as compared with the original parent cell strain, and, as a result, it increases the survival rate of individual mice (British Journal of Cancer, 1999, 80: 1115-1122, K. Satoh, et al.). Further, it is reported that the 67LR low-expression cell line retards tumor neovascularization and decrease, the production of a neovascularization promotion factor, VEGF itself, as compared with the parent strain (Cancer Letters, 2000, 153: 161-168, M. Tanaka, et al.). Similarly, also in tumor metastasis experiments using an antibody for 67LR, the same effect as in the antisense experiments has been recognized (Jpn. J. Cancer Res., 1999, 90: 425-431, K. Narumi, et al.).
In the fields not relating to tumor, some reports have been made regarding the function of 67LR. It is reported that the growth of neovascularized blood vessels that are induced in ischemic animal models is inhibited by a 67LR-binding laminin-derived peptide (cysteine-aspartic acid-proline-glycine-tyrosine-isoleucine-glycine-serine-arginine) or EGF-derived peptide (cysteine-valine-isoleucine-glycine-tyrosine-serine-glycine-aspartic acid-arginine-cysteine) (Am. J. Pathol., 2002, 160: 307-313, D. Gebarowska, et al.). It is reported that eNOS expression and NO production, which are said to participate in arteriosclerosis induced by the shear force to angioendothelial cells, are inhibited by a 67LR-binding laminin-derived pentapeptide (tyrosine-isoleucine-glycine-serine-arginine) (J. Biol. Chem., 1999, 274: 15996-16002, T. Gloe, et al.).
A recent report says that 67LR acts as a receptor for a prion protein, which is considered as a cause for Creutzfelds-Jakob disease, and prion binding for internalization and further the binding and the internalization are inhibited by secretion of a membrane domain-deficient mutant 67LR (EMBO J., 2001, 20: 5863-5875, S. Gauczynski, et al.).
It is also reported that 67LR is expressed in a subset group of CD4+CD8− or CD4−CD8+ of CD45RO+/CD45RA− memory cells that are a subset of T cells, and an effect of 67LR to the immune system is suggested (J. Immunol., 1999, 163: 3430-3440, S. M. Canfield, et al.).
There are some reports relating to the expression of mRNA of 67LR. It is reported that the expression is inhibited by a cancer-inhibiting factor p53 or anticancer factors TNF-alpha and IFN-gamma (Biochem. Biophys. Res. Commun., 1998, 251: 564-569, N. Clausse, et al.). However, there is no report relating to low-molecular compounds for 67LR which is presumed to participate in such diverse functions.
On the other hand, among catechins, epigallocatechin gallate (hereinafter this may be referred to as “EGCG”) is an main ingredient of tea catechins, accounting for about 50% thereof. In addition, tea catechins include epigallocatechin, epicatechin gallate and epicatechin (hereinafter these may be referred to as “EGC”, “ECG” and “EC”, respectively).
There is a long history that tea has been used as a drug from the past, and recently, tea has been analyzed for the relation between its efficacy and its components. Of the components, EGCG is a component discovered by A. Bradfield, et al. in 1947 (J. Chem. Soc., 1947, 32: 2249, A. E. Bradfield, et al.).
Various physiological effects of tea catechins including EGCG have been reported, for example, antioxidation, anticancer, suppression of plasma cholesterol increase, suppression of blood pressure increase, platelet aggregation inhibition, suppression of blood sugar increase, dementia prevention, antiulcer, antiinflammation, antiallergy, antibacterial, anticaries, antiviral, detoxication, enteroflora improvement, deodorization (Functions of Tea, edited by Keiichiro Muramatsu, Society Publishing Center, 2002).
Of those, there are many reports relating to anticancer effect that includes anti-mutation effect, anti-carcinogenic promotion effect, antitumor proliferation-inhibiting effect, anti-invasion/metastasis inhibiting effect, anti-neovascularization inhibiting effect. Recent reports say that EGCG inhibits DNA synthesis in leukemia cells, thereby inducing apoptosis (Int. J. Mol. Med., 2001, 7: 645-652, D. M. Smith, et al.), and that GCG inhibits the growth of breast cancer cells (J. Cell. Biochem., 2001, 82: 387-398, K. T. Kavanagh, et al.). Further, there is a report saying that EGCG inhibits the proliferation of cancer cells more strongly than that of normal cells (Arch. Biochem. Biophys., 2000, 376: 338-346, N. Ahmad, et al.).
Regarding invasion and metastasis, it is reported that catechin inhibits the invasion of high-metastatic cells in an invasion test using a matrigel, and that EGCG inhibits adhesion of cancer cells to fibronectin and laminin (Cancer Lett., 1995, 98: 27-31, M. Susuka, et al.; Cell Biol. Int., 1993, 17: 559-564, M. Isemura, et al.; Cancer Lett., 2001, 173: 15-20, Y. Suzuki, et al.).
Further, molecular-level analysis of these catechin effects has been reported recently. For example, EGCG concentration-dependently inhibits the proliferation of Her-2 antigen high-expression cells which, as suggested, may have relation to cancer. As reported, its functional mechanism would be inhibition of the downstream signal transmission through Her-2 phosphorylation inhibition (Cancer Res., 2002, 62: 652-655, S. Pianetti, et al.).
It has been reported that catechins including EGCG inhibit neovascularization which has close relationship with tumor growth. As indicated, the mechanism is that catechins inhibit the phosphorylation of VEGFR-1, a receptor for VEGF, which is a growth factor for angioendothelial cells. It is reported that this does not depend on the antioxidation and anti-radical activity of catechins (Cancer Res., 2002, 62: 381-385, S. Lamy, et al.).
Similarly, it is reported that catechins inhibit the phosphorylation of PDGF-R-beta by another growth factor, PDGF-BB in vascular smooth muscle cells, thereby inhibiting the hypertrophy of blood vessels (FASEB J., 2002, 16: 893-895, A. Sachinidis, et al.).
Further, it is reported that EGCG inhibits in-vivo neovascularization and growth of endothelial cells by EGF-2 (Nature, 1999, 389: 381, Y. Cao, et al.). There is a report saying that EGCG binds to an apoptosis-inducing Fas protein (Biochem. Biophys. Res. Commun., 2001, 285: 1102-1106, S. Hayakawa, et al.). However, it is not clarified as to whether the above-mentioned EGCG's effect could have relation to Fas, but suggesting the presence of any other factor that may interact with EGCG.
It has become clear on the molecular level that catechins have various physiological effects in addition to the antitumor effect thereof. It is reported that EGCG inhibits glucose production in hepatic cells and promotes tyrosine phosphorylation of the insulin receptor and IRS-1, and is therefore effective against diabetes (J. Biol. Chem., 2002, 277: 34933-34940, M. E. Waltner-Law, et al.).
From a report indicating that, in Parkinson model mice, EGCG shows a strong neuroprotective effect (J. Biol. Chem., 2002, 277: 30574-30580, Y. Levites, et al.), EGCG is expected to inhibit many types of neuropathy. There are a report saying that the expression of Fc-epsilon RI in basophils, which is a cause for allergy, is inhibited by EGCG and its methylated derivative (J. Agric. Food Chem., 2002, 50: 5729-5734, Y. Fujimura, et al.); and a report saying that the expression of COX-2 and NO synthase-2, as induced by IL-1-beta in cartilage, is inhibited by EGCG (Free Radical Biology & Medicine, 2002, 33: 1097-2002, S. Ahmed, et al.).
However, so long as the present inventors know, there is no report at all up to the present, relating to the fact that EGCG functions as a cell growth-inhibiting factor via 67LR and to the fact that 67LR may be used as a target in drug screening for low-molecular compounds having a cell growth-inhibiting effect.
(Non-Patent Reference 1)
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